- A novel and extremely simple UV–Vis spectroscopy technique for monitoring the ultrasound-driven exfoliation of single wall carbon nanotubes (SWNTs) in an aqueous solution of a surfactant is described. The principle of the method is based on the fact that only individual SWNTs absorb UV and visible light. Approaching a plateau value in the UV–Vis absorption, recorded as a function of time and/or the total ultrasonic energy supplied to the system, indicates that the maximum degree of exfoliation has been achieved. Accordingly further energy input should be avoided in order to prevent undesired damage of the SWNTs. Scanning electron microscopy pictures confirm that the leveling off of the absorbance corresponds to the maximum exfoliation of SWNTs. The proposed combination of absorption and imaging techniques offers a cheap, reliable and a viable method for monitoring SWNT exfoliation, assessable to almost all research groups.